A glass ionomer cement which is used mainly in the dentistry is prepared by setting a fluoroaluminosilicate glass powder and a polycarboxylic acid such as polyacrylic acid in the presence of water, and a set body thereof has transparency and is aesthetically excellent. Further, it has no irritant action to a dental pulp and excellent biocompatibility. Still further, it exhibits an excellent adhesion to any of enamel and dentin tooth substances, is good in marginal sealing, and can maintain durability in the mouth over a long period of time. Even further, since the glass powder contains fluorine, one can expect that it has a tooth substance-strengthening function. In view of these characteristics, the dental glass ionomer cement is widely used in various applications such as restoration and filling of dental cavity, cementing of prosthesis and orthodontic band, lining of dental cavity, core construction, pit and fissure sealant.
However, with respect to this glass ionomer cement, when a polyacrylic acid aqueous solution and a fluoroaluminosilicate glass powder are merely combined and mixed, the mixed material is low in fluidity and is poor in workability. Further, it requires a long period of time for setting, and a surface thereof is broken by the contact with saliva, whereby not only the surface of the cement becomes weak but also its final strength is not satisfactory.
In order to overcome these defects, a number of methods have been investigated. For example, Japanese Laid-Open Patent No. 101893/1977 discloses a method by which the above-described defects are solved and the characteristics of the glass ionomer cement are exhibited, i.e., it discloses a setting liquid comprising a 45-60% aqueous solution of polyacrylic acid or an acrylic acid copolymer having incorporated therein to from 7 to 25%, based on the total weight, of one or more of a polybasic carboxylic acid. Further, the present applicant disclosed in Japanese Laid-Open Patent No. 2210/1982 a dental glass ionomer cement setting liquid comprising a 45-55% aqueous solution of an acrylic acid/maleic acid copolymer having incorporated therein to from 10 to 25% of tartaric acid and from 0.1 to 5% of at least one fluorocomplex salt, based on the total weight. Still further, various other attempts have been made. In accordance with these methods, not only physical properties but also workability and water resistance are improved.
While various improvements of the dental glass ionomer cement have been investigated, the fluidity of the mixed paste is still insufficient as compared with that of a zinc phosphate cement which has hitherto been widely used and, therefore, it cannot yet be said that the workability is in an ideal state. In particular, when the glass ionomer cement is used for cementing of prosthesis, the flow is so poor that the cement film is likely to thicken and, hence, there was often found no fitting of the prosthesis. That is, at the time when the manipulation can be performed immediately after the mixing, it is necessary to increase the fluidity of the cement without lowering the physical properties. Further, when the glass ionomer cement is used for the filling, since it is inferior in physical properties such as crushing strength as compared with dental amalgams or dental composite resins, a glass ionomer cement which will be further improved in crushing strength is needed depending upon symptoms.